1. Field of the Disclosure
The present disclosure relates to deposition of metals and metal nitride thin films. In particular, the disclosure concerns methods of using periodic plasma annealing during an atomic layer deposition process.
2. Description of the Related Art
The integration level of components in integrated circuits is increasing rapidly, which demands a decrease of the size of integrated circuit (IC) components and interconnects. The trend of decreasing feature size is evident, for example, in memory circuits or devices such as dynamic random access memories (DRAMs), flash memory, static random access memories (SRAMs), ferroelectric (FE) memories, and integrated circuit components, such as gate electrodes and diffusion barriers in complementary metal oxide semiconductor (CMOS) devices.
Deposition methods available for forming metal and metal nitride films include atomic layer deposition (ALD), sometimes called atomic layer epitaxy (ALE). ALD processes include, without limitation, thermal ALD processes and plasma enhanced ALD (PEALD) processes, wherein plasma-excited species of a source material are used during certain processing steps. In some cases, an ALD process may include both thermal and PEALD processes.
In a typical thermal ALD process, a substrate is sequentially and alternately contacted with vapor phase pulses of two or more reactants. The reactants are alternately and sequentially pulsed into a reaction space comprising the substrate, which is maintained at an elevated temperature. The substrate temperature is high enough to overcome an energy barrier, such as, for example, the activation energy, during collisions between chemisorbed species on the surface and reactant molecules in the gas phase but low enough to avoid decomposition of the reactants. The pulsing sequence is repeated to form a metal film of desired thickness. Due to the self-limiting nature of ALD, films are grown at rate of about one monolayer (ML) per deposition cycle.
Existing thermal ALD techniques can typically achieve good step-coverage deposition or conformality of metal and metal nitride films, but they can result in high film resistivity and high impurity levels. For example, oxygen and halide impurities can be introduced into ALD films, especially at low deposition temperatures. High oxygen and halide incorporation in metal films can have a negative impact on film resistivity and/or other electrical properties, such as work function.
Existing PEALD techniques can achieve metal and metal nitride film deposition with comparatively good film properties, such as, for example, low resistivity and low impurity levels. However, PEALD typically produces low resistivity and low impurity films at the expense of poorer step coverage relative to thermal ALD. PEALD techniques also typically call for a long period of plasma exposure or plasma-on time during ALD cycles.